Heat developable light-sensitive materials often contain a base or a base precursor in order to accelerate heat development. And it is preferred to use a base precursor that releases a base by thermal decomposition for obtaining a good storage stability of the light-sensitive material.
Typical examples of base precursors are described in British Pat. No. 998,949. A preferred base precursor is a salt of a carboxylic acid and an organic base. Useful carboxylic acids are trichloroacetic acid and trifluoroacetic acid. Useful bases are guanidine, piperidine, morpholine, p-toluidine and 2-picoline. The guanidine trichloroacetic acid described in U.S. Pat. No. 3,220,846 is particularly useful. The aldoneamides described in Japanese Patent Application (OPI) No. 22625/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") are decomposed to generate bases at a high temperature and are used preferably.
However, the light-sensitive materials containing these base precursors often require a relatively long time to produce an image or have high fog. Moreover, these base precursors are susceptible to being affected by air or moisture and are subsequently decomposed to change the photographic properties of the light-sensitive material or impair its storage.